1. Field
An input device having a plurality of input keys whose outputs are detected by a variation in a resistance value is provided.
2. Related Art
Previously, an input device which includes a plurality of input keys and whose output varies in an analog manner according to a variation in pressing force applied to the input key has been provided.
Each input key whose output varies according to a variation in the pressing force applied thereto is composed of a resistor formed on a substrate and an elastically deformable contact disposed opposite to the resistor. The contact is formed of a material having a smaller specific resistance than that of the resistor. When the input key is operated to cause the contact to be pressed against the resistor, the resistance value varies due to a variation in the contact area between the contact and the resistor, which causes the voltage of the input key to vary.
It is possible to determine the operational states of all the input keys of the input device by detecting the voltages of the input keys within a predetermined period of time.
FIG. 9 is a diagram that illustrates an output detecting operation of a conventional input device. In the output detecting operation shown in FIG. 9, an input device provided with twelve input keys K1 to K12 is used as an example. In the diagram shown in FIG. 9, a vertical axis indicates a voltage value V (output) of the input keys K1 to K12, and a horizontal axis indicates a selection holding time T required for detecting the outputs of the input keys. In FIG. 9, the further the distance from the origin to the top becomes in the vertical axis, the larger the voltage value becomes. In addition, the further the distance from the origin to the right becomes in the horizontal axis, the larger the time value becomes.
As shown in FIG. 9, in the input device, output detection starts on the basis of the voltage of the input key K1, and the output detection is performed on the basis of the voltage of the input key K2 after a predetermined selection holding time T10 has elapsed. Then, the outputs of the input keys K3 to K12 are sequentially detected on the basis of the voltages of the input keys K3 to K12 whenever the selection holding time T10 elapses.
As shown in FIG. 9, the voltage values of the input keys K1, K2, K3, K6, K9, K10, K11, and K12 are equal to each other and are higher than those of the input keys K4 and K7. Therefore, the input keys K1, K2, K3, K6, K9, K10, K11, and K12 are in non-operational states. On the other hand, the voltage values of the input keys K4 and K7 are lower than those of the input keys K1, K2, K3, K6, K9, K10, K11, and K12. Therefore, the input keys K4 and K7 are in operational states. Thus, FIG. 9 shows that the input keys K4 and K7 are in the operational states.
The input keys K5 and K8 whose outputs are detected next to the input keys K4 and K7 in the operational states have low voltages during a period from the beginning to the middle of the selection holding time T10, but the voltages thereof gradually rise from the middle of the selection holding time T10 and reach the same voltage as that of the input keys K1, K2, K3, K6, K9, K10, K11, and K12. The reason is the input keys K5 and K8, which are in the non-operational states, are affected by the variation in the voltages of the input keys K4 and K7 whose outputs have already been detected, so that the voltages thereof are lowered to the same voltage as that of the input keys K4 and K7 whose outputs have already been detected, during a part of the selection holding times T10; however, the voltages of the input keys K5 and K8 are stabilized after the part of the selection holding time T10 has elapsed, so that the original voltages of the input keys K5 and K8 are output.
It is possible to determine the operational state of the input device by detecting the outputs of the input keys K1 to K12 for every predetermined selection holding time T10, on the basis of the voltages of the input keys K1 to K12, so as to check which of the input keys K1 to K12 is operating.
JP-A-2003-271291 discloses a technique for determining the operational state of an input device by determining the operational states of a plurality of input keys during a predetermined period of time.
In the conventional input device shown in FIG. 9, the outputs of the input keys K4 and K7 in operational states are detected for a predetermined selection holding time T10. The input keys K5 and K8, which are in the non-operational states, are affected by a variation in the voltages of the input keys K4 and K7 whose outputs have already been detected. It is necessary to secure a predetermined waiting time required to stabilize the voltages. Thus, the outputs of the input keys K5 and K8 are detected in the selection holding time T10.
In the conventional input device shown in FIG. 9, it is difficult to recognize which of the input keys K1 to K12 is in an operational state or which of the outputs of the input keys K1 to K12 is detected next to the input key that is in the operational state. Therefore, the output detection is performed on all the input keys K1 to K12, including an input key in an operational state and another input key whose output will be detected next to the input key in the operational state, for the same selection holding period T10.
It requires a lot of time to detect the outputs of all the input keys K1 to K12, which makes it difficult to perform output detection at high speed.